ec57 lab manual

Communication Systems Lab

EINSTEINCOLLEGE OF ENGINEERINGSir.C.V.Raman Nagar, Tirunelveli-12

Department of Electronics & Communication Engg

EC 57-COMMUNICATION SYSTEMS LAB

Name : ………………………………………

Reg No : ………………………………………

Branch : ………………………………………

Year & Semester : ………………………………………

of 87©Einstein College of Engineering


INDEX

EX.NO. DATE NAME OF THE EXPERIMENTSPage

no.MARKS

REMARKS

1 Amplitude modulation and Demodulation

2 Frequency modulation and Demodulation

3 Sampling techniques

4 Pulse Modulation-PAM

5 Pulse Modulation-PWM

6 Pulse Code Modulation

7 Time Division Multiplexing

8 Line Coding Techniques

9 Amplitude Shift Keying

10 Phase Shift Keying

11 Frequency Shift Keying

12 Quadrature Phase Shift Keying

13 Delta Modulation

14 Differential PCM

15 Phase Locked Loop

16 Pre-Emphasis/ De-Emphasis

17 Error Control coding using MATLAB



18 Chracteristics of AM Receiver-Study

19



Experiment No : 1 Date :

AMPLITUDE MODULATION & DEMODULATION

AIM:

To construct a Amplitude modulator circuit & demodulate the Amplitude

modulated wave.

COMPONENTS REQUIRED:

S.NO COMPONENTS RANGE

1) Transistor BC 107

2) Diode IN4001

3) Capacitors 0.01µF, 0.1µF,10µF

4) Resistors 22KΩ, 10KΩ,1.2KΩ,1.1KΩ

5) CRO

6) Bread Board,power

supply

7) Connecting Wires

THEORY :

The modulation is simply a method of combining two different signals and is used in the transmitter section of a communication system. The two signals that are used are the information signal and the carrier signal. Amplitude Modulation is the simplest form of signal processing in which the carrier amplitude is simply changed according to the amplitude of the information signal hence the name Amplitude modulation. When the information signals amplitude is increased the carrier signals amplitude is increased and when the information signals amplitude is decreased the carrier signals amplitude is



AMPLITUDE MODULATION CIRCUIT DIAGRAM:

DEMODULATION CIRCUIT DIAGRAM:



Decreased. The purpose of any detector or demodulator is to recover the original modulating signal with the minimum of distortion and interference. The simplest way of dealing with an AM signal is to use a simple half- wave rectifier circuit. If the signal were simply passed through a diode to a resistive load, the output would be a series of half-cycle pulses at carrier frequency. So the diode is followed by a filter, typically a capacitor and resistor in parallel. The capacitor is charged by the diode almost to the peak value of the carrier cycles and the output therefore follows the envelope of the amplitude modulation.

PROCEDURE:

1. Circuit connections are given as shown in the circuit diagram.2. The power supply is connected to the collector of the transistor.3. Using AFO the carrier signal is given to the base of the transistor.4. The modulating (message or base band) signal is given to the emitter of the

transistor.5. From the collector of the transistor, the modulated wave is noted down using

CRO.6. By varying the amplitude of the modulating signal the values of Emax and Emin are

noted down to find the modulation index.7. The amplitude modulated wave is now given as the input to the detector circuit.8. The demodulated (message) wave amplitude and frequency is noted down from

the CRO.



MODEL GRAPH:

OBSERVATION:

Amplitude Time Frequency m

Message Signal

Carrier signal

AM signal



Demodulated Signal

VIVA QUESTIONS:

1.What is meant by Modulation?2.Define Modulation index(m).3.Applications of AM4.Types of Demodulation of AM.5.What is the band width for AM?

RESULT:

Amplitude Modulator and Demodulators are constructed and its waveforms are

analyzed by using the above circuits.



FREQUENCY MODULATION CIRCUIT DIAGRAM:

FM DEMODULATOR:




FREQUENCY MODULATION & DEMODULATION

AIM:To construct & Design Frequency modulator using IC XR2206 & demodulate the

Frequency modulated wave by using IC565.

COMPONENTS REQUIRED:


8) Integrated Circuits IC X R2206, IC

NE565

9) Resistors

10) Capacitors

11) Function Generator 0 – 1 Mhz

12) DSO

13) Bread Board

14) Connecting Wires

THEORY : Frequency modulation is also called as angle modulation. Frequency modulation

is defined as changing the frequency of the carrier with respect to the message

signal amplitude. Here the amplitude of the carrier remains fixed & timing

parameter frequency is varied. When the modulating signal has zero amplitude,

then the carrier has frequency of Fc as amplitude of the modulating signal

increases. The frequency of the carrier increases, similarly, as the amplitude of

the modulating signal decreases, the frequency of the carrier decreases.



PIN DIAGRAM (XR-2206):

MODEL GRAPH



The modulation index is defined as the ratio of the maximum frequency

deviation to the modulating frequency. The maximum frequency deviation is

the shift from center frequency Fc when the amplitude of the modulating signal is

maximum.

By Carlson’s rule BW = 2 (F+ Fm(max))

Where F = Maximum frequency deviation

Fm(Max) = Maximum modulating frequency

MODULATION PROCEDURE:

Connections are given as per the circuit diagram.

Measure the carrier signal frequency at the pin2 of IC XR2206.

Apply modulating AF signal at pin7 of IC XR2206.

Observe the frequency-modulated signal on DSO.

Calculate the modulation index.

Calculate the BW.

DEMODULATION PROCEDURE:

Connections are made as per the circuit diagram.

Modulated signal is given as the input to 565.

In demodulated output the original message signal is recovered.



OBSERVATION:

Amplitude Time Frequency

Message Signal

Carrier signal

FM signal

Demodulated Signal

VIVA QUESTIONS:

1.What is meant by FM?2.Define Frequency Deviation.3.Applications of FM4.Types of Angle Modulation.5.What is the band width for FM?

RESULT:

Frequency Modulator and Demodulators are constructed and its waveforms are

analyzed by using CRO.



SAMPLING CIRCUIT DIAGRAM

PIN DIAGRAM:




SAMPLING TECHNIQUES

AIM:

To obtain the sampled version of given analog signal using operational amplifier and draw the spectrum.

APPARATUS REQUIRED:

THEORY:

The Sample and Hold circuit uses two buffers to keep a voltage level stored in a capacitor. Ssample will charge the capacitor to the present signal level, while the input buffer ensures the signal won't be changed by the charging process. From there, the output buffer will make sure that the voltage level across the storage cap won't decrease over time. Sclear will short out the storage cap, discharging it and setting the output to 0V.In actual practice, the switches used are various forms of transistor switch, which provides cleaner switching and also allows another circuit to control the sample and clearing operations. Excellent Sample and Hold circuits like the LF398 are available on a single chip for cheap and easy use.

Sample and Hold circuits are used internally in Analog to Digital conversion. We might also use them to hold a given signal value from any particular sensor on a robot, for analysis and later use.


Apparatus Range Quantity

IC741 2

FET BFW10 2

Capacitor 0.01µF 1

RPS 1

CRO 1

FG 1

Bread board 1


PROCEDURE:

The sample and hold circuit is assembled with the desired components. The input signal is given to the circuit from the function generator. The amplitude of the input signal should not exceed 10 volts. The frequency of the input signal is set to 600 Hz. The frequency of the sample signal is set to 5600 Hz. The next sample available is zero order holding device, integrate the signal between consequence sampling inputs.

VIVA QUESTIONS:

1.What is the need for sampling?2.Define sampling.3.Define Nyquist rate.4.What is the usage of capacitor in the circuit diagram?5.What is zero order hold?

RESULT:

Thus the sample and hold circuit output is obtained using OP- amp.



PAM CIRCUIT DIAGRAM:

MODULATION CIRCUIT:

DEMODULATION CIRCUIT:

Experiment No: 4 Date :



PULSE MODULATION – PAM

AIM:

To generate pulse amplitude modulated signals and demodulates it to get the original signal.

APPARATUS REQUIRED:

THEORY:

In pulse amplitude modulation, the amplitudes of regularly spaced rectangular pulses vary with the instantaneous sample values of a continuous message signal in a one to one fashion. The pulse in PAM can be of rectangular or the type that we have arrival in natural sampling. The carrier under goes amplitude modulation in PAM. The width of the pulse remains fixed. Natural sample method is used here to generate the PAM signal. The diodes are used as a switching element. If the closing time t of the diode approaches zero, the output gives only the instantaneous value. Since the width of the pulse approaches zero. The instantaneous sampling gives train of impulses. The area of each sampled section is equal to the instantaneous value of the signal input. This signal is modulated with the message signal. Thus we get the PAM output.

MODEL GRAPH:



Transistor 2N2222 1

Resistor 10Kohm 2

22Kohm 3

Capacitor 0.1µF 3

CRO 1

FG 2

Bread board 1


PROCEDURE:



1. Make connections as shown in the diagram. 2. Set the input signal and carrier signal.3. Obtain PAM signal 4. Measure the amplitude and frequency5. Demodulate the PAM signal.

TABULATION:


Message Signal

Carrier signal

PAM signal

Demodulated Signal

VIVA QUESTIONS:

1.Define PAM.2.What is frame in PAM?3.What is aperture effect?4. What is the need for speech coding at low bit rates?5. What do you mean by companding? Define compander.

RESULT:

Thus the PAM signal is obtained and the original signal is demodulated from PAM signal.

PWM CIRCUIT DIAGRAM:



MODULATION CIRCUIT:



PULSE MODULATION – PWM



AIM:

To generate pulse width modulated signals and demodulates it to get the original signal.

APPARATUS REQUIRED:

THEORY:

The PWM is also known as pulse duration modulation. It modulates the time parameter of the pulses. The width of PWM pulses varies. The amplitude is constant; width of the pulse is proportional to the amplitude of the modulating signal. Bandwidth on transmission channel depends on rise time of the pulse. The demodulation circuit used is a simple filter circuit that demodulator the PWM signal and gives the original message input.

MODEL GRAPH:



IC 555 1

Resistor 47Kohm 1

10Kohm 1

Capacitor 0.01µF 1

RPS 0-30v 1

CRO 1

FG 1

Bread board 1


PROCEDURE:



1. Make connections as shown in the diagram. 2. Set the input signal and carrier signal.3. Obtain PWM signal 4. Measure the amplitude and frequency5. Obtain the demodulated output.

TABULATION:


Message Signal

Carrier signal

PWM signal

Demodulated Signal

VIVA QUESTIONS:

1.Define PWM.2. What is the disadvantage of uniform quantization over the non-uniform Quantization?3.Define deviation ratio4.What is carrier recovery?5.Define bandwidth efficiency.

RESULT:

Thus the PWM signal is obtained and the original signal is demodulated from PWM signal.

CIRCUIT DIAGRAM:



MODULATION CIRCUIT:





PULSE CODE MODULATION

AIM:

To generate pulse code modulated signals and demodulates it to get the original signal.

APPARATUS REQUIRED:

THEORY:

Pulse Code modulation come under digital communication technique. In PCM the message signal is represented by a sequence of coded pulse which accomplished by representing the signal in discrete form in both time and amplitude.

PCM consist of a receiver and transmitter part. Transmitter section consists of sampler, quantizer, encoder and parallel to serial converter. Receiver part consists of serial to parallel set converter. Digital to analog converter and LPF are constituted as receiver part. Sampling, Quantizing and Encoding operations are performed in the same circuit which is called as analog to digital converter.

PROCEDURE:

1. Make connections as shown in the diagram. 2. Set the start of conversion switch from low to high and high to low.3. Set the input signal and obtain the PCM signal.4. Obtain the demodulated output.5. Measure the data and plot the graph.



PCM kit VCT07 1

CRO 1

Patch card


TABULATION:

Message Signal:

PCM Signal:

Demodulated Signal:


Amplitude in Time in Frequency in

Amplitude in ON Time in OFF Time in Frequency in



VIVA QUESTION:

1.Write the equation for probability of error

2.Define quadbit

3.Explain M-ary

4.State the concept of PCM

5.PCM is analog or digital modulation ,Explain.

RESULT:

Thus the PCM signal is obtained and the original signal is demodulated from PCM signal.



BLOCK DIAGRAM:



Experiment No :7 Date :

TIME DIVISION MULTIPLEXING

AIM:

To obtain time division multiplexed signal from different channel and make it to transmit in a single channel.

APPARATUS REQUIRED:

THEORY:

Time Division multiplexing is a digital process that can be applied when the data rate capacity of the transmission medium is greater than the data rate required by the sending and receiving devices. In such a case, multiple transmission can occupy a single link by subdividing them and interleaving the portions. TDM can be implemented in two ways. Synchronous TDM and Asynchronous TDM. In synchronous, the multiplexer allocates exactly the same time slot to each device at all times whether or not a device has anything to transmit.

PROCEDURE:

1. Make connections as shown in the diagram. 2. Adjust the potentiometer to set the input signal. 3. View the modulated output.4. Obtain the demodulated output.5. Measure the data and plot the graph.



TDM kit VCT02 1

CRO 1

Patch card


TABULATION:

Message Signal:

Carrier Signal:

Modulated Signal:

Demodulated Signal:







VIVA QUESTIONS:

1.What are the 4 primary causes for ISI?

2.What is Multiplexing?

3.State the concept for TDM.

4.Explain the ideal channel noise.

5.What is coding efficiency.

RESULT:

Thus the TDM signal is obtained and the original signal is demodulated from TDM signal.



BLOCK DIAGRAM




LINE CODING TECHNIQUES

AIM:

To obtain the standard digital codes from the source coded signals using various techniques.

APPARATUS REQUIRED:

THEORY:

In digital systems, the electrical waveforms are coded representations of the original information. If the original information is an analog signal, this must be converted to a series of discrete values that can be transmitted digitally. The process of converting the original information into a data sequence is referred to as source coding.

The line coding is the process of converting source coded signals into standard digital codes for the purpose of transmission over the channel. There are many possible ways of assigning the waveforms into the digital data. Simplest form of coding is ON-OFF, where a ‘1’ is transmitted by a pulse and a ‘0’ is transmitted by no pulse. Generally the line coding is used in transmitter section while decoding in receiver section. The line decoding is the process of converting standard digital codes into source coded waveforms.



Trainer kit VCT37 1

CRO 1

Patch card


Various line coding formats are

1. Unipolar RZ2. Polar RZ3. Polar NRZ4. Bipolar NRZ5. Bipolar RZ6. Manchester coding

PROCEDURE:

1. Connect the PRBS (test point P5) to various line coding formats. Obtain the coded output as per the requirement.

2. Connect coded signal test point to corresponding decoding test point as inputs. 3. Set the SW1 as per the requirement.4. Set the potentiometer P1 in minimum position.5. Switch ON the power supply. Press the switch SW2 once.6. Display the encoded signal on one channel of CRO and decoded signal on

second channel of CRO.



MODEL GRAPH:



TABULATION:

No Coding techniques ON time OFF time

1 Unipolar RZ

2 Polar RZ

3 Polar NRZ

4 Bipolar NRZ

5 Bipolar RZ

6 Manchester coding

VIVA QUESTIONS:

1.What are the different types of coding techniques for digital data?

2.State the concept of Manchester coding.

3.Differentiate polar and bipolar.

4.What is codec?

5.Explain Line coding.

RESULT:

Thus the various line encoding and decoding techniques were studied and the corresponding waveforms were drawn by using VCT-37 trainer kit.



CIRCUIT DIAGRAM:

MODULATION CIRCUIT:




AMPLITUDE SHIFT KEYING

AIM:

To generate ASK modulated and demodulated signal.

APPARATUS REQUIRED:

THEORY:

ASK or ON-OFF key is the simplest digital modulation technique. In this method there is only one unit energy carrier it is switched ON/OFF depending upon the input binary sequence to transmit symbol 0 & 1. No pulse is transmitted output contains some complete no of cycle of carrier frequency.

The disadvantage of ASK is the modulated carrier signal is not continuously transmitted. The peak power requirement is also high. The bit error probability rate is also not required in this technique.

PROCEDURE:

1. Make connections as shown in the diagram. 2. Set the input signal and carrier signal.3. Obtain ASK signal 4. Measure the amplitude and frequency5. Obtain the demodulated output.



Trainer kit VCT17 1

CRO 1

Patch card


MODEL GRAPH:

.



TABULATION:

INPUT DATA:

CARRIER SIGNAL:

MODULATED SIGNAL:

DEMODULATED SIGNAL:


Amplitude in ON Time in OFF Time in





PROGRAM FOR ASK:



VIVA QUESTIONS:

1.Define OOK.

2.Define information capacity

3.What is the Baud rate for ASK?

4.What is Digital Transmission?

5. Why do we go for Gram-Schmidt Orthogonalization procedure?

RESULT:

Thus the modulated and demodulated signal was obtained for amplitude shift keying techniques



BLOCK DIAGRAM




PHASE SHIFT KEYING

AIM:

To obtain the modulated and demodulated output waveform by using Phase Shift Keying technique.

APPARATUS REQUIRED:

THEORY:

PSK is a digital modulation scheme which is analogues to phase modulation. In binary phase shift keying two output phases are possible for a single carrier frequency one out of phase represent logic 1 and logic 0. As the input digital binary signal change state the phase of output carrier shift two angles that are 180o out of phase.

In a PSK modulator the carrier input signal is multiplied by the digital data. The input carrier is multiplied by either a positives or negatives consequently the output signal is either +1sinw ct or -1sinwct. The first represent a signal that is phase with the reference oscillator the latter a signal that is 180o out of phase with the reference oscillator. Each time a change in input logic condition will change the output phase consequently for PSK the output rate of change equal to the input rate range and widest output bandwidth occurs when the input binary data are alternating 1/0 sequence. The fundamental frequency of an alternate 1/0 bit sequence is equal to one half of the bit rate.

PROCEDURE:

1. Make connections as shown in the diagram. 2. Set the input signal and carrier signal.3. Obtain PSK signal 4. Measure the output data and draw the graph.5. Obtain the demodulated output.



PSK Kit VCT21 1

CRO 1

Patch cards


MODEL GRAPH:

.

:



TABULATION:

INPUT DATA:

CARRIER SIGNAL:

MODULATED SIGNAL:

DEMODULATED SIGNAL:







PROGRAM FOR PSK:



VIVA QUESTIONS:

1.Explain Coherent detection

2.Difference between PSK and FSK

3.Advantages of PSK

4. What is maximum likelihood detector?

5.What is correlator?

RESULT:

Thus the modulated and demodulated signal was obtained for phase shift keying techniques.



FSK CIRCUIT DIAGRAM:




FREQUENCY SHIFT KEYING

AIM:

To obtain the modulated and demodulated output waveforms by using hardware kit and in Matlab program for Frequency Shift Keying technique.

APPARATUS REQUIRED:

THEORY:

In digital data communication, binary code is transmitted by shifting a carrier frequency between two preset frequencies. This type of transmission is called frequency shift keying technique. A 555 timer in astable mode can be used to generate FSK signal. The standard digital data input frequency is 150Hz. When input is HIGH, transistor Q is off and 555 timer works in the normal astable mode of operation.

fo=1.45/(Ra+2Rb)c



IC 555 1

Transistor BC547 1

Resistor47Kohm 1

10Kohm 1

Potentiometer 50Kohm 2

Capacitor 0.01µF 2

FG 1

RPS 1

CRO 1


MODEL GRAPH:

THEORETICAL CALCULATION:



PROGRAM:



TABULATION:

INPUT DATA:

CARRIER SIGNAL:

MODULATED SIGNAL:




Symbol Amplitude Time period No.of cycle Frequency

Symbol 1

Symbol 0


PROCEDURE:

1. Make connections as shown in the circuit diagram. 2. Set the input signal and carrier signal.3. Obtain FSK signal 4. Tabulate the output data and draw the graph.5. Justify the obtained output with theoretical calculation.

VIVA QUESTIONS:

1.What are the Different types of Digital modulation?

2.Define PSK,QPSK.

3.Advantage of PSK over ASK&FSK?

4.What is base band signal receiver?

5.Define h-factor in FSK

RESULT:

Thus the Frequency Shift Keying modulated output waveform is obtained and it is justified with theoretical calculation.



BLOCK DIAGRAM:

QPSK MODULATOR:

QPSK DEMODULATOR




QUADRATURE PHASE SHIFT KEYING

AIM:

To obtain the modulated and demodulated output waveforms by using hardware kit and by Matlab program for Quadrature phase Shift Keying technique.

APPARATUS REQUIRED:

THEORY:

QPSK is another form of angle-modulated, constant-amplitude digital modulation. It is an M-ary encoding technique where M=4. with QPSK four output phases are possible for a single carrier frequency. Two bits (a dibit) are clocked into the bit splitter. After both bits have been serially inputted, they are simultaneously parallel outputted. One bit is directed to the I channel and the other to the Q channel. The I bit modulates a carrier that is in phase with the reference oscillator and the Q bit modulates a carrier that is 900 out of phase with the reference carrier. QPSK modulator is two BPSK modulators combined in parallel.

The input QPSK signal is given to the I and Q product detectors and the carrier recovery circuit. The carrier recovery circuit produces the original transmit carrier oscillator signal. The recovered carrier must be frequency and phase coherent with the transmit reference carrier. The QPSK signal is demodulated in the I and Q product detectors, which generate the original I and Q data bits. The output of the product detectors are fed to the bit combining circuit, where they are converted from parallel I and Q data channels to a single binary output data stream.



QPSK Kit VCT29 1

CRO 1

Patch cards


MODEL GRAPH:



PROGRAM:



TABULATION:

INPUT DATA:

CARRIER SIGNAL:

PROCEDURE:

1. Connect the binary input data to I-channel.2. Connect the binary input data to Q-channel.3. Connect the sine wave input to balanced modulator (I channel) as a carrier signal and

to sine wave input to balanced modulator (Q channel) as a carroer signal.4. Switch on the power supply.5. Display binary input data on CRO. Adjust pot1 and pot3 to get bipolar data.6. Adjust gain control pot to set equal amplitude in I and Q channel.7. Obtain QPSK signal. 8. Connect the QPSK to input of QPSK demodulator.9. Obtain the demodulated QPSK signal.

RESULT:

Thus the Quadurate Phase shift Keying modulated and demodulated output waveform is obtained.





BLOCK DIAGRAM:

DM MODULATOR:

DM DEMODULATOR:




DELTA MODULATION

AIM:

The objective of this equipment is to examine and study the technique of delta modulation and demodulation.

APPARATUS REQUIRED:

THEORY:

Delta modulation transmits only 1 bit per sample. The modulator comprises of comparator, quantizer and integrator. With conventional PCM, each code is a binary representation of both the sign and magnitude of a particular sample, therefore multiple-bit code is required to represent a one sample. With DM, rather than transmit a coded representation of the sample, only a single bit is transmitted, which simply indicates whether that the sample is larger or smaller than the previous sample. If the current sample is smaller than previous sample, a logic level 0 is transmitted. If the current sample is larger than the previous sample, a logic 1 is transmitted.

PROCEDURE:

1. Switch on the power supply. Ensure that the following initial condition exits on VCT-32a. Keep the signal ON/OFF switch in OFF position.b. Keep all potentiometer controls in min.

2. Set the sine wave by adjusting OFFSET and AMP 3. Vary the sine wave from 150Hz. Note that the amplitude of sine wave decreases at 2KHz

of frequency 4. Set clock frequency as 8KHz. Turn ON the left side ON/OFF switch and right side

ON/OFF, now adjust the offset control signal. Note down the quantizer output, integrated output and biphase NRZ encoder.

5. Obtain the modulated output. Connect modulator output to demodulator input.6. Obtain the demodulated output.



QPSK Kit VCT32 1

CRO 1

Patch cards


MODEL GRAPH:



TABULATION:

INPUT DATA:

INTEGRATOR SIGNAL:

MODULATED SIGNAL:

DEMODULATED SIGNAL:







VIVA QUESTIONS:

1.Define delta modulation.

2.What is slope over load?

3.Define Granular noise.

4.Define Adaptive DM.

5.How the noises are reduced in DM?

RESULT:

Thus the delta modulated and demodulated waveforms were obtained.



BLOCK DIAGRAM:

DPCM MODULATOR:

DPCM DEMODULATOR:




DIFFERENTIAL PULSE CODE MODULATION

AIM:

The objective of this equipment is to examine and study the technique of differential PCM and demodulation.

APPARATUS REQUIRED:

THEORY:

In a PCM Encoded waveform, there are often successive samples taken in which there is little difference between the amplitudes of the two samples. This necessitates transmitting several identical PCM codes, which is redundant. DPCM is designed specifically to take advantage of the sample to samples redundancies in such waveforms. With DPCM, the difference in the amplitude of two successive samples s transmitted rather than the actual sample. Because the range of sample differences is typically less than the range of individual samples. Fewer bits are required for DPCM than conventional PCM.

PROCEDURE:

1. Switch on the power supply. Keep DC voltage in minimum position2. Connect DC voltage and vary to 1.5v. Now display the output of zeros and ones in the

CRO.3. Obtain the modulated output. Now connect modulated output to demodulator input4. Now vary the DC control POT, the ADC coded data ranges which also reflects at the

output of the LATCH.



DM Kit VCT34 1

CRO 1

Patch cards


TRAINER KIT DIAGRAM:



MODEL GRAPH:



TABULATION:

INPUT DATA:

MODULATED SIGNAL:

DEMODULATED SIGNAL:






VIVA QUESTIONS:

1.Say the difference between PCM and DPCM.

2.Define Vocoder.

3.Bit rate of DPCM.

4.Define baseband transmission

5. Define Dibit.

RESULT:

Thus the differential PCM modulated and demodulated waveforms were obtained.



CIRCUIT DIAGRAM:




PHASE LOCKED LOOP

AIM:

To study the characteristics of Phase Locked Loop .

APPARATUS REQUIRED:


1) Transistor BC 107

2) IC NE565, IC7490

3) Capacitors

4) Resistors

5) CRO


supply

7) Connecting Wires



DESIGN:

THEORY:

If an input signal Vs of frequency fs is applied to the PLL, the phase detector compares the phase and frequency of the incoming signal to that of the output Vo of the VCO. It the two signals differ in frequency and /or phase, an error voltage Ve is generated. The phase detector is basically a multiplier and produces the sum (fs+fo) and difference (fs-fo) components at its output. The high frequency component (fs+fo) is removed by the low pass filter and the difference frequency component is amplified and then applied as control voltage Vc to VCO. The signal Vc shifts the VCO frequency in a direction to reduce the frequency difference between fs and fo. The VCO continues to change frequency till its output frequency is exactly the same as the input signal frequency. The circuit is then said to be locked.



PIN DIAGRAM:

OBSERVATION:

f1=755Hz, f2=1640Hz, f3=1250Hz, f4=360Hz



PROCEDURE:

1. Make the circuit connection as shown in Fig 1.2. Measure the practical free running frequency of VCO for zero input.3. Set the input square wave of 1Vp-p at 1KHz.4. Increase the input frequency till PLL is locked. This frequency f1 gives the lower end of

the capture range. Go on increasing the input frequency to f2 (upper end of the lock range), till PLL tracks the input signal.

5. Now gradually decrease the input frequency till f3 when the PLL is again locked. This is the upper end of the capture range. Keep on decreasing the input frequency till f4 when the loop is unlocked. This is the lower end of the lock range.

6. Compare theoretical and practical values of lock range and capture range.

VIVA QUESTIONS:

1.What is VCO?

2.Define Lock range,Capture range.

3.What are the applications of PLL?

4.Define PLL.

5.What is frequency synthesizer?

RESULT:

Thus the PLL characteristics are studied

Theoretical Lock range fL= Theoretical Capture range fC=

Practical Lock range fL= Practical Capture range fC=



CIRCUIT DIAGRAM:

PRE-EMPHASIS:

DE-EMPHASIS:




PRE-EMPHASIS / DE-EMPHASIS

AIM:

Design and conduct an experiment to test a pre-emphasis and de-emphasis circuit for

75Ps between 2.1KHz to 15KHz and record the results.

APPARATUS REQUIRED:


1) IC IC741

2) Capacitors

3) Resistors

4) CRO


supply

6) Connecting Wires

PROCEDURE:

1. Connections are made as shown in the circuit diagram.

2. Apply a sine wave of 5Vpp amplitude, vary the frequency and note down the gain of the circuit.

3. Plot a graph of normalized gain Vs frequency.



DESIGN

1. Pre-emphasis circuit.

Given f1 = 2.1 KHz, f2 = 15KHz.

f1 = 1/2SrC, f2 = 1/2SRC

Choose C = 0.1Pf then r = 820 and R = 100.

Also r/R = Rf/R1, then R1 = 2.2K and Rf = 15K.

2. De-emphasis circuit.

fC = 1/2SRdCd.

Choose Cd = 0.1Pf and fC = f1 = 2.1KHz

Then Rd = 820.

MODEL GRAPH:



TABULATION:

PRE-EMPHASIS:

Vi=

Frequency(Hz)

VO Gain= VO/ Vi Gain in dB

DE-EMPHASIS:

Vi=

Frequency(Hz)

VO Gain= VO/ Vi Gain in dB



VIVA QUESTIONS:

1.What is advantage of FM over Am?

2.Define Pre-emphasis and De-emphasis.

3.Define capture effect.

4.What are the types of FM?

5.Define transmission efficiency.

RESULT:

Thus the Pre-Emphasis and De-Emphasis circuit was designed and analysed using IC741.




ERROR CONTROL CODING USING MATLAB

AIM:

To write a program in MATLAB for error control coding techniques.

ALGORITHM:

1.Get the input binary sequcence.

2.Calculate the reundancy bits for the corrosponding code.

3.Transmit the signal that contains message bits+redundancy bits added at the end.

4.Calculate the redundancy bits once again for the received bits.

5.If the redundancy bits=’0’ then no error in the transmission otherwise some error in

the transmission.



PROGRAM:



RESULT:

Thus the error control coding techniques are executed using MATLAB programs.




CHARACTERISTICS OF AM RECEIVER

AIM:

To study the characteristics of AM receiver.

APPARATUS REQUIRED:

1. VCT 06KIT.2. CRO3. Patch card.

THEORY:

Heterodyne means to mix two frequencies together in a non-linear device or to translate one frequency to another frequency using non-linear mixing. The first section is the RF section which consists of a predictor is a broad tuned BPF with an adjustable centre frequency that is tuned to the desired carrier frequency. Selectivity is a receiver parameter that is used to measure the ability of the receiver to accept a given band of frequencies and reject all others. For example, with the commercial AM broadcast band, each station’s transmitter is allocated a 10KHz bandwidth. Therefore, for a receiver to select only those frequencies assigned to a single channel, the receiver must limit its bandwidth to 10KHz. If the pass band is greater than 10KHz, more than one channel may be received and demodulated simultaneously. If the pass band of a receiver is less than 10KHz, a portion of the modulating signal information for that channel is rejected or blocked from entering the demodulator and, consequently lost.

PROCEDURE:

1. Switch ON the trainer kit.2. Initial setup is made as follows.

a. Set audio oscillator frequency as 1KHz and amplitude as 1Vp-pb. Adjust the carrier frequency of AM transmitter to one position.c. Adjust the gain of the audio amplifier in some position.



BLOCK DIAGRAM:



TABULATION:

No dB Bandwidth

1 -3

2 -60

1. Now tune the gang capacitance in the preselector block, such that the output is of maximum amplitude.

2. Connect CRO across test point and find out -3db bandwidth of IF amplifier. Also find out -60db bandwidth of IF amplifier

3. Calculate Shape factor for various input signal.

VIVA QUESTIONS:

1.Define Selectivity.

2.What is sensitivity?

3.Define Q factor in AM receiver.

4.What are the three noises present in the AM reciver?

5.Define shape factor.

RESULT :

Thus the characteristics of the AM receiver is studied.


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